Formation of conductive connection tracks in package mold body using electroless plating

ABSTRACT

A first packaged semiconductor device is provided. The first packaged semiconductor device includes a first semiconductor die having a first terminal, a first electrically conductive lead that is electrically connected to the first terminal, and a first electrically insulating mold compound that encapsulates the first semiconductor die and exposes an end portion of the first lead at an outer surface of the first mold compound. A conductive track is formed in the outer surface of the first mold compound. Forming the conductive track includes activating a portion of the outer surface of the first mold compound for an electroless plating process, and performing the electroless plating process so as to form an electrically conductive material only within the activated portion of the outer surface of the first mold compound.

TECHNICAL FIELD

The instant application relates to semiconductor devices, and inparticular relates to techniques for electrically connecting one or morepackaged semiconductor device together.

BACKGROUND

Integrated circuit devices, such as semiconductor chips, are commonlypackaged using a lead frame and encapsulant material, such as a moldingcompound. For example, one or more semiconductor chips may be physicallyattached and electrically connected to a lead frame, e.g., usingconductive bond wires. The encapsulant material is formed around thesemiconductor chip and electrical connections. The encapsulant protectsthe semiconductor chip and electrical connections from damagingenvironmental conditions, such as moisture, temperature, foreignparticles, etc. The leads of the lead frame are externally accessiblefrom outside of the encapsulant material, and in some cases protrudeaway from the encapsulant material. These outer portions of the leadsprovide external electrical terminals that allow the packaged device tobe electrically connected to a printed circuit board, for example.

Many semiconductor processing technologies utilize lead frame strips tosimultaneously package a number of semiconductor devices. A lead framestrip includes a number of unit lead frames continuously repeated on asheet conductor, with openings in the sheet conductor defining thefeatures of the unit lead frames. Each unit lead frame provides the leadconstruction for a single packaged device. One or more semiconductordies can be affixed to and electrically connected with each unit leadframe. The unit lead frames are singulated from one another to formindividual packaged devices. The encapsulant material may be molded onthe lead frame before or after the unit lead frames are singulated.

An important design consideration for many semiconductor applications isspace efficiency. In many cases, the available space for a packagedsemiconductor device is severely limited. Techniques for optimizingspace efficiency include chip-stacking solutions. However, thesetechniques suffer from various drawbacks. For instance, direct slackingof chips within a package is limited by the available area of the diepad and the size of the semiconductor dies. Adequate cooling representsanother challenge in these package styles, as only one of the two chipsis in direct contact with the heat sink portion of the package (i.e.,the die pad). Another solution involves the stacking of two distinctpackaged semiconductor devices on top of one another. With stackedpackaged devices, electrical interconnection between the two devicesrepresents a notable challenge. Electrical connection between the twodevices can be done using a so-called interposer. However, thisinterposer adds cost, complexity and increases the overall thickness ofthe design.

SUMMARY

A method of forming a semiconductor package is disclosed. According toan embodiment of the method, a first packaged semiconductor device isprovided. The first packaged semiconductor device includes a firstsemiconductor die having a first terminal, a first electricallyconductive lead that is electrically connected to the first terminal,and a first electrically insulating mold compound that encapsulates thefirst semiconductor die and exposes an end portion of the first lead atan outer surface of the first mold compound. A conductive track isformed in the outer surface of the first mold compound. Forming theconductive track includes activating a portion of the outer surface ofthe first mold compound for an electroless plating process, andperforming the electroless plating process so as to form an electricallyconductive material only within the activated portion of the outersurface of the first mold compound.

According to another embodiment of the method, a first packagedsemiconductor device is provided. The first packaged semiconductordevice includes a first semiconductor die having a first terminal, afirst electrically conductive lead that is electrically connected to thefirst terminal, and a first electrically insulating mold compound thatencapsulates the first semiconductor die and exposes an end portion ofthe first lead at an outer surface of the first mold compound. Aconductive track is formed in the outer surface of the first moldcompound. The first electrically insulating mold compound includes amulti-layer exterior compound that includes: a metallic ion containinglayer, a hydrophilic layer disposed on the metallic ion containinglayer, and a hydrophobic layer disposed on the hydrophilic layer.

An electronic circuit is disclosed. The electronic circuit includes afirst packaged semiconductor device having a first semiconductor dieincluding a first terminal, a first electrically conductive lead that iselectrically connected to the first terminal, and a first electricallyinsulating mold compound that encapsulates the first semiconductor dieand exposes an end portion of the first lead at an outer surface of thefirst mold compound. A conductive track is formed in the outer surfaceof the first mold compound.

Those skilled in the art will recognize additional features andadvantages upon reading the following detailed description, and uponviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The elements of the drawings are not necessarily to scale relative toeach other. Like reference numerals designate corresponding similarparts. The features of the various illustrated embodiments can becombined unless they exclude each other. Embodiments are depicted in thedrawings and are detailed in the description which follows.

FIG. 1, which includes FIGS. 1A and 1B, illustrates a packagedsemiconductor device, according to an embodiment. FIG. 1A depicts aside-view of the packaged semiconductor device and FIG. 1B depicts aplan-view of the packaged semiconductor device.

FIG. 2, which includes FIGS. 2A and 2B, illustrates forming a conductivetrack in the mold compound of the packaged semiconductor device. FIG. 2Adepicts a bottom side of the packaged semiconductor device beforeforming the conductive track and FIG. 2B depicts a bottom side of thepackaged semiconductor device after forming the conductive track.

FIG. 3 depicts a close-up view of a multi-layer exterior mold compoundthat is configured for a laser structuring and electroless platingtechnique, according to an embodiment.

FIG. 4 depicts patterning the hydrophobic layer using a laser, accordingto an embodiment.

FIG. 5 depicts removing a portion of the hydrophilic layer that isexposed by the patterned hydrophobic layer, according to an embodiment.

FIG. 6 depicts performing an electroless plating process to form aconductive track in a recessed portion of the multi-layer exterior moldcompound, according to an embodiment.

FIG. 7 depicts a side view of a multi-chip packaged semiconductordevice, according to an embodiment.

FIG. 8 depicts first and second circuit assemblies that include leadframes, semiconductor dies, and electrically conductive bond wires,according to an embodiment.

FIG. 9 depicts a side view of the multi-chip packaged semiconductordevice with conductive tracks in the mold compound electricallyconnecting the leads of the first and second circuit assemblies,according to an embodiment.

FIG. 10, which includes FIGS. 10A and 10B, depicts a method for forminga multi-package stack with conductive tracks providing an electricalconnection between the various packages of the multi-package stack. FIG.10A depicts a first packaged semiconductor device with conductive tracksformed in the mold compound and FIG. 10B depicts a second packagedsemiconductor affixed to the first packaged semiconductor device andelectrically connected to the conductive tracks.

DETAILED DESCRIPTION

Embodiments described herein include a method of forming a conductivetrack in the mold body of a packaged semiconductor device. According tothis technique, a packaged semiconductor device with an electricallyinsulating mold compound is provided. The mold compound encapsulates atleast one semiconductor die and the associated electrical connections(e.g., wire bonds) between the semiconductor die and a first lead. Aconductive track is formed in the electrically insulating mold compound.

By forming the conductive track in the mold body of a packagedsemiconductor device according to the presently disclosed techniques, avariety of advantageously space efficient package designs are madepossible. For example, the conductive tracks can be used to provide acompact package design whereby two opposite facing circuit assembliesare molded together in a single package. In this package, separate leadframes, which may be identical to one another, can be provided at topand bottom sides of the package. The die pads for the opposite facingsemiconductor dies can be exposed at the top and bottom sides of thepackage. Thus, each semiconductor chip can be independently cooled usingseparate heat sinks. The conductive tracks can be formed to provide avertical electrical connection between the top and bottom facing leadsat the outside of the package. In another advantageous embodiment, twodiscrete packaged devices are directly adhered to one another. One ofthe packages includes the conductive tracks to provide electricalconnection between the leads of both devices. The conductive tracksadvantageously eliminate the need for an interposer, and thus reducepackage thickness and cost.

Formation of the conductive track in the mold body of a packagedsemiconductor device is made possible by a laser structuring processthat activates the mold compound for an electroless plating process.According to this technique, the electrically insulating mold compoundof the packaged device includes a multi-layer exterior compound that isspecifically tailored for a laser structuring process. The multi-layerexterior includes a metallic ion containing layer, a hydrophilic layerdisposed on the metallic ion containing layer, and a hydrophobic layerdisposed on the hydrophilic layer. Through a sequence of laserpatterning and etching, a structured portion of the metallic ioncontaining layer can be exposed to the exterior environment. After thissequence, an electrical conductor is formed in the structured portion ofthe multi-layer exterior compound using an electroless depositionprocess. In this way, the electrical conductor can be selectively formedin the activated portion of the mold compound without being formed onother surfaces of the mold compound.

Referring to FIG. 1, a packaged semiconductor device 100 is depicted,according to an embodiment. The packaged semiconductor device 100includes a semiconductor die 102 having electrically conductiveterminals 104, a plurality of electrically conductive leads 106, a diepad 108, and a plurality of electrical connections 110 between the leads106 and the terminals 104 of the die. An electrically insulating moldcompound 112 encapsulates the semiconductor die 102 and the electricalconnections 110 and exposes end portions of the leads 106. In FIG. 1, atransparency view of the mold compound 112 is used so that the interiorcomponents of the packaged semiconductor device 100, i.e., thesemiconductor die 102, the electrical connections 110, etc., can beseen.

In general, the semiconductor die 102 can be any active or passiveelectronic component. Examples of these devices include powersemiconductor devices, such as power MISFETs (Metal InsulatorSemiconductor Field Effect Transistors) power MOSFETs (Metal OxideSemiconductor Field Effect Transistors), IGBTs (Insulated Gate BipolarTransistors), JFETs (Junction Gate Field Effect Transistors), HEMTs(High Electron Mobility Transistors), power bipolar transistors or powerdiodes such as, e.g., PIN diodes or Schottky diodes, etc. Other examplesof these devices include logic devices, such as microcontrollers, e.g.,memory circuits, level shifters, etc.

The terminals 104 of the semiconductor die 102 are externallyaccessible. These terminals 104 may include the input, output andcontrol terminals of the device. For instance, in the example of aMOSFET device, the terminals 104 may include gate, source and drainterminals 104. These terminals 104 can have any of a wide variety ofshape and configuration. These terminals 104 can be formed fromelectrical conductors such as Cu, Ni, NiSn, Au, Ag, Pt, Pd, In, Sn, andalloys thereof.

The semiconductor die 102 can be configured as a so-called lateraldevice. In this configuration, the semiconductor die 102 has its loadterminals (e.g., source and drain terminals) disposed on a single mainsurface (e.g., as depicted) and is configured to conduct in a directionthat is parallel to the main surface of the semiconductor die 102.Alternatively, the semiconductor die 102 can be configured as aso-called vertical device. In this configuration, the device has itsload terminals 104 disposed on opposite facing main and rear surfacesand is configured to conduct in a direction that is perpendicular to themain and rear surfaces.

The die pad 108 and the leads 106 of the packaged semiconductor device100 can be collectively provided from a lead frame. The die pad 108serves as a chip carrier that physically supports and is adhered to thesemiconductor die 102. Adhesion between the semiconductor die 102 andthe die pad 108 can be provided by a wide variety of techniquesincluding solder, adhesive tape, glue, etc. The electrically conductiveleads 106 are physically separated and electrically isolated from oneanother and from the die pad 108. The lead frame that includes the leads106 and the die pad 108 can be formed from any of a wide variety ofelectrically conductive materials, including copper, aluminum, andalloys thereof.

The electrical connections 110 between the terminals 104 the firstsemiconductor die 102 and the conductive leads 106 can be provided byelectrically conductive bond wires. These bond wires may be attached andelectrically connected to the semiconductor die 102 and the leads 106using a solder material, for example. More generally, any of a varietyof electrical connection techniques can be utilized to effectuate theseelectrical connections 110 including, e.g., conductive ribbons, PCB,conductive traces, etc.

Generally speaking, the electrically insulating mold compound 112 caninclude a wide variety of electrically insulating materials that aresuitable for semiconductor packaging. Examples of these materialsinclude thermoset materials or thermoplastic materials which specialformulated with non-active metal. The non-active metal ions can beactivated, e.g., using the laser activation process to be discussedbelow. Thermoplastic materials may include one or more materialsselected from the group of polyetherimide (PEI), polyether-sulfone(PES), polyphenylene-sulfide (PPS), polyamide-imide (PAI), andpolyethylene-terephthalate (PET). Thermoplastic materials may includeone or more materials selected from the group of polyetherimide (PEI),polyether-sulfone (PES), polyphenylene-sulfide (PPS), polyamide-imide(PAI), and polyethylene-terephthalate (PET). Thermoplastic materialsmelt by application of pressure and heat during molding or laminationand (reversibly) harden upon cooling and pressure release.

The mold compound 112 encapsulates the first semiconductor die 102 andthe electrical connections 110 between the first semiconductor die 102and the leads 106. That is, the mold compound 112 encloses the firstsemiconductor die 102 and the electrical connections 110 such that theseitems are protected from the exterior environment. End portions of theleads 106 are exposed from the outer surface 114 of the mold compound112. That is, the end portions of the leads 106 are externallyaccessible for electrical connection thereto from outside of the firstpackaged semiconductor device 100, e.g., from an external printedcircuit board. Additionally, a lower side of the die pad 108 is exposedat the outer surface 114 of the mold compound 112. In this way, the diepad 108 can serve as an electrical terminal as well as a heat sink thatis configured to transfer heat generated by the first semiconductor die102 to an external apparatus, e.g., a heat sink provided in an externalprinted circuit board. In other embodiments, the lower side of the diepad 108 may be encapsulated by the mold compound 112.

Referring to FIG. 2, a conductive track 116 is formed in the outersurface 114 of the mold compound 112, according to an embodiment. Inthese figures, the mold compound 112 is opaque so that the interiorcomponents of the first packaged semiconductor device 100 are notvisible.

Referring to FIG. 2A, a bottom side of the packaged semiconductor device100 is shown. The bottom side includes the end portions of the leads 106that are exposed from the mold compound 112. In this figure, the moldcompound 112 is opaque so that the interior components of the firstpackaged semiconductor device 100 are not visible.

Referring to FIG. 2B, a conductive track 116 is formed in the outersurface 114 of the mold compound 112, according to an embodiment. Theconductive track 116 includes an electrically conductive material thatcan provide a low-ohmic electrical connection. In the depictedembodiment, the conductive track 116 is formed to directly contact oneof the leads 106. Thus, the conductive track 116 may, but does notnecessarily, form an electrical connection with one of the terminals 104of the semiconductor die 102 via by a lead 106 that is electricallyconnected to the semiconductor die 102. Alternatively, the conductivetrack 116 may form an electrical connection with an unassigned lead,i.e., a lead that is disconnected from the semiconductor die 102.According to yet another embodiment, the conductive track 116 iscompletely electrically isolated from all of the leads 106.

Referring to FIG. 3, a close up cross-sectional view of the moldcompound 112 is depicted, according to an embodiment. This mold compound112 is specifically formulated for a laser structuring and electrolessplating process. The mold compound 112 includes a multi-layer exteriorcompound 118 that is formed on the base mold compound 120. The base moldcompound 120 may include any of the aforementioned mold compound 112materials that are conducive to a transfer or injection molding process,e.g., thermoset materials or thermoplastic materials.

The multi-layer exterior compound 118 includes a metallic ion containinglayer 122 that is disposed on the base mold compound 120. The metallicion containing layer 122 is a layer of mold material, e.g., plastic thatincludes metallic ions that are suitable for an electroless depositionprocess. For example, in one embodiment, the metallic ion layer 122contains palladium ions (Pd²⁺).

The multi-layer exterior compound 118 additionally includes ahydrophilic layer 124 disposed that is disposed on the metallic ioncontaining layer 122. A hydrophilic layer 124 refers to a layer that isdissolvable by a fluid such as a wet chemical etchant. Exemplarymaterials for the hydrophilic layer 124 include materials from theR-000H carbonyl group.

The multi-layer exterior compound 118 additionally includes ahydrophobic layer 126 disposed on the that is disposed on thehydrophilic layer 124. A hydrophobic layer 126 refers to a layer that isresistant to dissolution or deterioration by a fluid such as a wetchemical etchant. Exemplary materials for the hydrophobic layer 126include materials from the hydrocarbon group (CH4).

Referring to FIG. 4, the hydrophobic layer 126 is patterned. That is, aportion of the hydrophobic layer 126 is removed in a predefinedgeometry. In this way, an underlying portion of the hydrophilic layer124 is exposed from the hydrophobic layer 126 in the patterned shape ofthe hydrophobic layer 126. According to an embodiment, this patterningis done using a laser. The laser process is carried out in such a way tocompletely remove the portion of the hydrophobic layer 126 withoutsubstantially removing the hydrophilic layer 124.

Referring to FIG. 5, a portion of the hydrophilic layer 124 that isexposed by the patterned hydrophobic layer 126 is removed so as toexpose a patterned region of the metallic ion containing layer 122. Thisremoval step may be done using a wet chemical etch technique, whereinhydrophobic layer 126 acts as an etch mask, and the etch is selective tothe material of the metallic ion containing layer 122. Exemplarychemical eichant materials include sodium hydroxide (NaOH) or potassiumhydroxide (KOH).

As a result of the laser patterning and etching steps described withreference to FIGS. 4 and 5, a recessed channel 128 is formed in theouter surface 114 of the mold compound 112. A recessed channel 128refers to a local depression in the mold compound 112 that is beneaththe adjacent planar surfaces in the mold compound 112. The recessedchannel 128 exposes the metallic ion containing layer 122 and thereforeprovides an activated portion of the mold compound 112 that is suitablefor an electroless plating process. The sidewalls of this recessedchannel 128 may be, but are not necessarily, parallel to one another.

Referring to FIG. 6, an electroless plating process is performed. Asused herein, an electroless plating process refers to a process thatutilizes a plating solution with a chemical reaction agent that reactswith metal ions in the plating solution to form a metal coating. By wayof comparison, an electroless metal plating process differs from anelectroplating technique, which utilizes a current source to attractmetal ions to the article. In general, any of a variety of electrolessplating processes can be formed to provide a conductive metal trace inthe activated portion of the mold compound 112, i.e., the exposedportion of the metallic ion containing layer 122. These conductivematerials can include a wide variety of metals, such as nickel,palladium, gold, silver, copper, and alloys thereof. According to anembodiment, the electroless plating process is a Nickel-Phosphorous(NiP) process, and more particularly, may be aNickel-Molybdenum-Phosphorous (NiMoP) plating process. In this process,the packaged semiconductor device 100 is submerged in an electrolessplating solution. Generally speaking, the plating solution can be anyautocatalytic reducing agent that is chemically reactive with a metalion. Examples include hydrated sodium hypophosphite (NaPO₂H₂.H₂O). Inthe case of an electroless Nickel-Molybdenum-Phosphorous (NiMoP) platingprocess, the plating solution can include a mixture of sodiumhypophosphite and a solution containing nickel sulphate, molybdenum,boric acid and citric acid, such as an an M20 solution, which is made byBASF®. As a result of the chemical reaction that occurs between themetallic ion containing layer 122 and the electroless plating solution,a conductive metal, e.g., nickel-phosphorous forms in the recessedchannel 128. Meanwhile, the conductive metal does not form on the moldcompound 112 outside of the recessed channel 128, as these regions ofthe mold compound 112 are chemically inactive.

Advantageously, the laser structuring technique enables a wide varietyof geometries and configurations for the conductive track 116. Thenumber, orientation and geometry of the conductive track 116 (or tracks)can vary substantially. Moreover, the conductive track 116 may be formedon multiple faces of the mold compound 112. The only constraints placedon the geometry and configuration of the conductive track 116 are thoseimposed by the laser structuring process as described above. That is,the conductive track 116 can be formed in any shape that is feasible bythe laser patterning and etching sequence. Various examples theconductive track 116 used in a multi-chip arrangement will be describedin further detail below with reference to FIGS. 7-10.

Referring to FIG. 7, a packaged semiconductor device 200 is depicted.The packaged semiconductor device 200 includes first and secondsemiconductor dies 202, 203. Each of the first and second semiconductordie 202, 203 may be configured as the semiconductor dies 102 previouslydiscussed with reference to FIG. 1. The packaged semiconductor device200 includes first and second lead frames, with each of the first of thesecond lead frames containing a die pad 208 and a plurality ofelectrically conductive leads 206. These lead frames may be configuredas the lead frame previously discussed with reference to FIG. 1. Thefirst lead frame is disposed on a bottom side of the packagedsemiconductor device 200 such that a lower side of the die pad 208 andthe ends of leads 206 of the first lead frame are exposed at the bottomsurface 234 of the mold compound 212. The second lead frame is disposedon a top side of the of the packaged semiconductor device 200 such thata lower side of the die pad 208 and the ends of leads 206 of the secondlead frame are exposed at the top surface 236 of the mold compound 212.A first terminal of the first semiconductor die 102 is electricallyconnected to a lead 206 from the first lead frame, e.g., in a similarmanner as previously described with reference to FIG. 1. A secondterminal of the second semiconductor die 102 is electrically connectedto a lead 206 from the second lead frame, e.g., in a similar manner aspreviously described with reference to FIG. 1.

In the packaged semiconductor device 200 of FIG. 7, the first and secondsemiconductor dies 202, 203 are vertically spaced apart from oneanother. That is, the upper surfaces of the first and secondsemiconductor dies 202, 203 that face one another do not contact oneanother at all. Instead, the mold compound 212 is provided between theupper surfaces of the first and second semiconductor dies 202, 203.

Referring to FIG. 8, a process step in a method for forming the packagedsemiconductor device 200 of FIG. 7 is depicted. According to thismethod, first and second circuit assemblies 218, 220 are provided. Thefirst circuit assembly includes a first lead frame 222 having the firstdie pad 208 and a first plurality 207 of the electrically conductiveleads 206. A plurality of the electrical connections 210 is providedbetween the first semiconductor die 202 and some of the leads 206 in thefirst plurality 207. In particular, a first lead 206 a in the firstplurality 207 is electrically connected to the first terminal of thefirst semiconductor die 202 by one of the electrical connections 210.The second circuit assembly includes a second lead frame 224 having asecond die pad 208 and a second plurality 209 of the electricallyconductive leads 206. A plurality of the electrical connections 210 isprovided between the second semiconductor die 203 and some of the leads206 in the second plurality 209. In particular, a second lead 206 b inthe second plurality 209 is electrically connected to the secondterminal of the second semiconductor die 203 by one of the electricalconnections 210.

After the first and second circuit assemblies 218, 220 are provided inthe above described manner, the second circuit assembly 220 is arrangedabove the first circuit assembly 210 such that the second semiconductordie 203 faces and is vertically spaced apart from the firstsemiconductor dies 202. That is, the first and second circuit assemblies218, 220 are vertically stacked on top of one another, with the bottomside of the first lead frame 222 facing away from the bottom side of thesecond lead frame 224. In other words, the first and secondsemiconductor dies 202, 203 are sandwiched in-between the bottom sidesof the first and second lead frames 222, 224. Moreover, the secondcircuit assembly is held in a position such that the secondsemiconductor die 203 does not contact the first semiconductor dies 202.According to one embodiment, the first circuit assembly 218 is providedusing a pre-molded lead frame that includes a ring of electricallyinsulating mold compound 212 formed around the periphery of the firstlead frame 222. This ring of electrically insulating mold compound 212provides a support mechanism for the second lead frame 224 to rest uponwhen placed over the first lead frame 222, while maintaining aseparation between the first and second semiconductor dies 202, 203.

Referring to FIG. 9, after the first and second circuit assembles arearranged on top of one another as described above, the mold compound 212is formed over the first and second semiconductor dies 202, 203. Themold compound 212 can be formed according to any of a variety oftechniques. According to an embodiment, a compression molding techniqueis used to form the mold compound 212 in this manner. The mold compound212 is formed in such a way that the first and second semiconductor dies202, 203 and the associated electrical connections 210 to the leads 206are encapsulated by the mold compound 212. Meanwhile, portions of thefirst and second lead frame 222, 224 are exposed at the outer surface ofthe mold compound 212, e.g., in the manner previously described withreference to FIG. 7. Moreover, the mold compound 212 is formed toinclude the multi-layer exterior compound 118 as previously describedwith reference to FIG. 3.

After the mold compound 212 is formed, a laser structuring technique isperformed in the manner previously described with reference to FIGS.4-6. As a result, a plurality of conductive track 216 are formed. Inthis embodiment, the conductive tracks 216 are formed to extend along asidewall of the mold compound 212 that extends between the oppositefacing top and bottom surfaces 236, 234 of the mold compound 212, theleads 206 from the first plurality and the leads 206 from the secondplurality. The conductive tracks 116 form direct electrical connectionsbetween the leads 206 from the first plurality 207 that is associatedwith the first lead frame 222 and the leads 206 from the secondplurality 209 that is associated with the second lead frame 224.

According to the depicted embodiment, one of the conductive tracks 216forms a direct electrical connection between the second lead 206 b inthe second plurality 209 that is electrically connected to the secondterminal of the second semiconductor die 203 and one the second leads206 in the first plurality 207 that is electrically disconnected fromthe second semiconductor die 202. In this way, electrical access to theterminals of the second semiconductor die 203 can be provided at thebottom side 214 of the mold compound 212. Thus, electrical access to allterminals of the first and second semiconductor dies 202, 203 can beprovided at the bottom side 214 of the mold compound 212.

According to another embodiment (not shown), one of the conductivetracks 216 forms a direct electrical connection between the second lead206 b in the second plurality 209 that is electrically connected to thesecond terminal of the second semiconductor die 203 and the first lead206 a in the first plurality 207 that is electrically connected to thefirst terminal of the first semiconductor die 202. In this way, theconductive track 216 is used to form a direct electrical connectionbetween the terminals of the first and second semiconductor dies 202,203. Referring to FIG. 10, first and second packaged semiconductordevices 300, 301 are provided. Each one of the first and second packagedsemiconductor devices 300, 301 can have any of the configurations of thepackaged semiconductor device 100 described with reference to FIG. 1 orthe package configuration described with reference to FIGS. 7-9. In thedepicted embodiment, the first packaged semiconductor device 300 is aso-called OF (quad flat) package with externally accessible leads on alower side of the package that are coplanar with the molding material.In addition, the second packaged semiconductor device 301 so-calledsurface mount package with externally accessible leads that protrudeaway from a side of the molding material. According to anotherembodiment (not shown), the first packaged semiconductor device 300 canbe substantially similar or identical to the packaged semiconductordevice 200 described with reference to FIGS. 7-9 with leads disposed ontop and bottom sides of the package and multiple semiconductor diesencapsulated within the package.

Conductive tracks 316 are formed in the mold compound 312 of the firstpackaged semiconductor device 300. These conductive tracks 316 may beformed using the laser structuring and electroless plating process aspreviously described with reference to FIGS. 3-6. The conductive tracks316 are formed to extend from some of the leads 306 of the firstpackaged semiconductor device 300 to the die attachment site 340. Theseconductive tracks 316 may contact “unassigned” leads 306, i.e., leads306 that are disconnected from the semiconductor die (or dies) that ispackaged within the first packaged semiconductor device 300.Alternatively, these conductive tracks 316 may contact leads 306 thatare connected to the terminals of the semiconductor die (or dies) thatis packaged within the first packaged semiconductor device 300.

The second packaged semiconductor device 301 is attached to the firstpackaged semiconductor device 300 such that the outer surface of themold compound 312 from the first packaged semiconductor device 300 isflush against the mold compound 314 from the second packagedsemiconductor device 301. In particular, a lower side (not shown) of themold compound 314 from the second packaged semiconductor device 301 isflush against the die attachment site 340 on the mold compound 312 fromthe first packaged semiconductor device 300.

The attachment of the second packaged semiconductor device 301 to thefirst packaged semiconductor device 300 can be done using a soldertechnique. For example, a solder material can be screen printed on themold compound 312 of the first packaged semiconductor device 300 to forma metallized pad in the die attachment site 340. Subsequently, apick-and-place technique is utilized to place the second packagedsemiconductor device 300 on the metallized pad 340. Subsequently, areflow process is performed to melt the solder and complete the adhesionbetween the first and second packaged semiconductor devices 300, 301.

Advantageously, the conductive tracks 316 enable a compact, stackedpackage design wherein the first and second packaged semiconductordevices 300, 301 are flush against one another. No interposer isrequired for electrical access to the second packaged semiconductordevice 301. Instead, the conductive tracks 316 enable electrical accessto the leads 306 of the second packaged semiconductor device 301 fromthe leads 306 of the first packaged semiconductor device 300. Thus, theterminals of the semiconductor die (or dies) in the second packagedsemiconductor device 301 can be electrically accessed from a printedcircuit board that directly contacts the leads 306 of the first packagedsemiconductor device 300 using the “unassigned” leads 306 of the firstpackaged semiconductor device 300. Further, the terminals of thesemiconductor die (or dies) in the second packaged semiconductor device301 can be directly electrically connected to the terminals of thesemiconductor die (or dies) in the first packaged semiconductor device300 using the connected leads 306 of the first packaged semiconductordevice 300.

The stacked package configuration shown in FIG. 10 represents just oneof a variety of potential configurations that are made possible by theconductive tracks 316 described herein. For example, one or both sidesof the first packaged semiconductor device 300 can accommodate multipleones of the second packaged semiconductor devices 301. In the case ofmultiple ones of the second packaged semiconductor devices 301 affixedto a single first packaged semiconductor device 300, the conductivetracks 316 can be used to connect these multiple second packagedsemiconductor devices 301 to one another, as well as to the leads 306 ofthe first packaged semiconductor device 300. In the embodimentsdescribed herein, a packaged semiconductor device 100 is used as anexemplary packaged device that is suitable for the formation ofconductive tracks 116 in the mold body (i.e., the portion of the devicethat includes the electrically insulating mold compound 112) accordingto the activation and electroless plating techniques described herein.The disclosed package design represents just one examples of a widevariety of packaged devices that are suitable for this technique. Moregenerally, the conductive track structures and corresponding methods forforming the conductive tracks are applicable to a wide variety ofpackage designs and materials. These packages can be so-called open aircavity style packages wherein the semiconductor dies and associatedelectrical connections are provided within an open air cavity that isenclosed by an electrically insulating mold compound and a protectivelid. Alternatively, these packages can be so-called molded packages(e.g., as depicted), wherein the mold compound is formed directly aroundthe semiconductor dies and associated electrical connections. Thesepackages can be so-called leaded packages wherein the electricallyconductive leads protrude away from the outer surface of the moldcompound so as to enable insertion of the lead into a receptacle, e.g.,a socket of a printed circuit board. Alternatively, these packages canbe so-called leadless packages (e.g., as depicted) wherein the exposedsurfaces of the leads are coplanar with the mold compound. Exemplarypackages types that are suitable for the conductive track structures andcorresponding methods for forming the conductive tracks include the DIP(dual in-line package) style packages, TO (transistor outline) stylepackages, QFP (quad-flat-package) style packages, surface mount stylepackages, etc., to name a few.

The term “electrically connected” as used herein describes a permanentlow-ohmic, i.e., low-resistance, connection between electricallyconnected elements, for example a wire connection between the concernedelements. By contrast, the term “electrically coupled” contemplates aconnection in which there is not necessarily a low-resistance connectionand/or not necessarily a permanent connection between the coupledelements. For instance, active elements, such as transistors, as well aspassive elements, such as inductors, capacitors, diodes, resistors,etc., may electrically couple two elements together.

Spatially relative terms such as “under,” “below,” “lower,” “over,”“upper” and the like, are used for ease of description to explain thepositioning of one element relative to a second element. These terms areintended to encompass different orientations of the device in additionto different orientations than those depicted in the figures. Further,terms such as “first,” “second,” and the like, are also used to describevarious elements, regions, sections, etc. and are also not intended tobe limiting. Like terms refer to like elements throughout thedescription.

As used herein, the terms “having,” “containing,” “including,”“comprising” and the like are open-ended terms that indicate thepresence of stated elements or features, but do not preclude additionalelements or features. The articles “a,” “an” and “the” are intended toinclude the plural as well as the singular, unless the context clearlyindicates otherwise.

It is to be understood that the features of the various embodimentsdescribed herein may be combined with each other, unless specificallynoted otherwise.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A method of forming a semiconductor package, themethod comprising: providing a first packaged semiconductor device, thefirst packaged semiconductor device comprising a first semiconductor diecomprising a first terminal, a first electrically conductive lead thatis electrically connected to the first terminal, and a firstelectrically insulating mold compound that encapsulates the firstsemiconductor die and exposes an end portion of the first lead at anouter surface of the first mold compound; mounting a second packagedsemiconductor device on top of the first packaged semiconductor device,the second packaged semiconductor device comprising a secondsemiconductor die having a second terminal, a second electricallyconductive lead that is electrically connected to the second terminal,and a second electrically insulating mold compound that encapsulates thesecond semiconductor die and exposes a portion of the second lead at anouter surface of the second mold compound; and forming a conductivetrack in the outer surface of the first mold compound, wherein thesecond packaged semiconductor device is mounted on top of the firstpackaged semiconductor device with the exposed portion of the secondlead contacting the outer surface of the first mold compound; whereinthe conductive track electrically connects the exposed portion of thesecond lead to the exposed portion of the first lead, wherein the moldcompound that encapsulates the first semiconductor die comprises ametallic ion containing layer; and wherein forming the conductive trackcomprises: activating the first mold compound by applying a laser to theouter surface of the first mold compound and exposing a portion of themetallic ion containing layer; forming an electrically conductivematerial only within the activated portion of the the first moldcompound.
 2. A method of forming a semiconductor package, the methodcomprising: providing a first packaged semiconductor device comprising afirst semiconductor die comprising a first terminal, a firstelectrically conductive lead that is electrically connected to the firstterminal, and a first electrically insulating mold compound thatencapsulates the first semiconductor die and exposes an end portion ofthe first lead at an outer surface of the first mold compound mounting asecond packaged semiconductor device on top of the first packagedsemiconductor device, the second packaged semiconductor devicecomprising a second semiconductor die having a second terminal, a secondelectrically conductive lead that is electrically connected to thesecond terminal, and a second electrically insulating mold compound thatencapsulates the second semiconductor die and exposes a portion of thesecond lead at an outer surface of the second mold compound; and forminga conductive track in the outer surface of the first mold compound,wherein the second packaged semiconductor device is mounted on top ofthe first packaged semiconductor device with the exposed portion of thesecond lead contacting the outer surface of the first mold compound;wherein the conductive track electrically connects the exposed portionof the second lead to the exposed portion of the first lead, wherein theconductive track electrically connects the exposed portion of the secondlead to the exposed portion of the first lead, and wherein the firstelectrically insulating mold compound comprises a multi-layer exteriorcompound comprising: a metallic ion containing layer, a hydrophiliclayer disposed on the metallic ion containing layer, and a hydrophobiclayer disposed on the hydrophilic layer.
 3. The method of claim 2,wherein forming the conductive track comprises patterning thehydrophobic layer using a laser, removing a portion of the hydrophiliclayer that is exposed by the patterned hydrophobic layer so as to form aa recessed channel of the metallic ion containing layer, and performingan electroless plating process that deposits an electrically conductivematerial in the recessed channel.
 4. A method of forming a semiconductorpackage, the method comprising: providing a first circuit assemblycomprising: a first lead frame, the first lead frame comprising a firstdie pad and a first plurality of electrically conductive leads, a firstsemiconductor die mounted on the first die pad, and a first plurality ofelectrical connections between the first semiconductor die and the firstplurality of electrically conductive leads; providing a second circuitassembly comprising: a second lead frame, the second lead framecomprising a second die pad and a second plurality of electricallyconductive leads, a second semiconductor die mounted on the second diepad, and a second plurality of electrical connections between the secondsemiconductor die and the second plurality of electrically conductiveleads; arranging the second circuit assembly above the first circuitassembly such that the second semiconductor die faces and is verticallyspaced apart from the first semiconductor die; forming a first moldcompound over the first and second semiconductor dies after thearranging of the second circuit assembly above the first circuitassembly such that the first and second semiconductor dies and therespective electrical connections between the first and secondsemiconductor dies and the first and second leads are encapsulated bythe first mold compound and such that end portions of the leads in thefirst and second pluralities are exposed at the outer surface of thefirst mold compound; and forming a conductive track in the outer surfaceof the first mold compound; wherein, after forming the first moldcompound, the end portions of the leads in the first and secondpluralities are exposed at opposite facing top and bottom sides of thefirst mold compound, wherein the conductive track is formed along asidewall of the first mold compound that extends between the oppositefacing top and bottom sides, wherein the conductive track forms a directelectrical connection between a lead from the first plurality of theleads and a lead from the second plurality of the leads, wherein thefirst mold compound that encapsulates the first semiconductor diecomprises a metallic ion containing layer, and wherein forming theconductive track comprises: activating a portion of the first moldcompound by applying a laser to the outer surface of the first moldcompound and exposing a portion of the metallic ion containing layer;and forming an electrically conductive material only within theactivated portion of the first mold compound.
 5. The method of claim 4,wherein arranging the second circuit assembly above the first circuitassembly comprises placing a ring of electrically insulating moldcompound formed around the periphery of the first lead frame prior toforming a first mold compound and placing the first lead frame on thering of electrically insulating mold compound, and wherein the ring ofelectrically insulating mold compound physically supports the secondcircuit assembly during the formation of the first mold compound.
 6. Themethod of claim 4, wherein the conductive track forms a directelectrical connection between a first lead from the first plurality thatis electrically connected to the first terminal of the firstsemiconductor die and a second lead from the second plurality that iselectrically connected to the second terminal of the secondsemiconductor die.
 7. The method of claim 4, wherein the conductivetrack forms a direct electrical connection between a first lead from thefirst plurality of the leads that is electrically connected to the firstterminal of the first semiconductor die and a third lead from the secondplurality of the leads that is electrically disconnected connected fromthe second semiconductor die.